Hydraulic, pneumatic, electric, and mechanical actuators generally include a housing and an actuation member. For example, a linear hydraulic actuator contains a hydraulic cylinder housing inside which a piston actuation member moves. In another example, a rotary vane actuator includes a housing inside which a vane-type actuation member rotates. In torque tubes having a similar construction, the vane-type actuation member can instead be stationary such that the housing rotates around the vane-type actuation member. Generally, in these actuators, bearings are often used to facilitate motion and prevent friction along the main linear or rotary axis. However, the axial bearings in rotary vane and torque tube actuators can, in some circumstances, wear on the actuation member seals, which can create actuation internal fluid leak paths resulting in actuator dead band.
A cross-sectional view of a conventional rotary vane actuator 10 is shown in FIG. 5. As can be seen in FIG. 5, the rotary vane actuator 10 includes a housing 12 and an actuation member, particularly two vanes 14. The vanes 14 rotate in the housing 12 about the axis defined by rotor 16. The vanes 14 rotate between a rotor cap 18 and a floor 20 of the housing 12. As seen in FIG. 5, seals 21 are provided around three sides of each vane 14 and seal the vane 14 to the rotor cap 18, the floor 20, and the walls of the housing 12. A first axial bearing 22 is interference fit into the rotor cap 18 and machined down to flush with the surface of the rotor cap 18. Similarly, a second axial bearing 24 is interference fit into to the floor 20 of the housing 12 and machined down to flush with the surface of the floor 20.
During operation, the first axial bearing 22 and the second axial bearing 24 tend to work loose from the rotor cap 18 and floor 20, respectively. This creates a ledge in the surface of up to several thousandths of an inch, and this ledge wears against the seals 21, wearing a groove into the seals 21. As mentioned above, this groove creates internal leak paths for the actuation fluid, resulting in actuator dead band and excess internal fluid leakage.
Embodiments of the present invention address the problems associated with bearing placement in actuators. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.